“Therefore lift your drooping hands and strengthen your weak knees.”

Have you ever seen a marathon runner that is very weary with their hands and arms hanging, shoulders drooping, knees and legs weak? This is the picture the author is painting.
The verse above is Hebrews 12:12. The author is saying that we who know Christ sometimes feel like giving up because of God’s discipline. However, because of Christ, we should pick up our hanging head and strengthen our weak knees. We have a source of power that the world does not. We should draw on the power of Christ when we feel we can’t go on. God will discipline those he loves, so that we will become more like his Son. God’s goal for us is not our temporal happiness or comfort, but for us to be conformed to the image of His Son Jesus Christ.
So the author is telling us that God’s discipline will make us feel weary and tired, but we are to respond to this discipline by turning from our sin, lifting our head and strengthening our knees. We are do to this, so God will no longer need to discipline us, allowing Him to better use us for the ministry of the Gospel of Jesus Christ.
Therefore, lift your drooping hands and strengthen your weak knees. Know that God is disciplining so you will turn from your sin back to Him. He loves you too much to let you live in sin, when you can be living in His freedom and peace.